Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $33.96   13.557%   $38.564   $38.56   $38.55   $38.60  
  Purchase #2 $92.36   3.559%   $95.6471   $95.65   $95.65   $95.60  
  Purchase #3 $123.72   11.246%   $137.6336   $137.63   $137.65   $137.60  
  Purchase #4 $200.32   11.241%   $222.838   $222.84   $222.85   $222.80  
  Purchase #5 $210.71   9.701%   $231.151   $231.15   $231.15   $231.20  
  Purchase #6 $21.27   5.823%   $22.5086   $22.51   $22.50   $22.50  
  Purchase #7 $119.90   7.662%   $129.0867   $129.09   $129.10   $129.10  
  7 purchase totals = $802.24       $877.4290   $877.43   $877.45   $877.40